Why is Panasonic the Only One that has a Fixed F-Stop thru Their Zoom Lens Range??

This IS unnatural, and this leads to another letdowns of the lens. No way

I mean that man who responded on me does not get it - once you have your lens full tele, you obviously have to get less light on the sensor. That way you must get more if you are on wide. If you don´t, some degradation siomewhere happens, and those speed changing lenses WILL win the battle on the end of this war for obvious reasons.
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Why does he do it?